Relationship of scientists and engineers on major experiments (especially particle physics)

I am interested in other academics’ experiences with large experiments (especially something like the LHC). To what extent do the “engineers” who design and build the machine (solder electronics, assemble quadrupole magnets, etc) interact with “scientists” who determine the program (who might want to test their 11-dimensional model etc)? Do the two sides take an active interest in each other’s work and give constructive suggestions to one another? Are the technicians all hired locally? How many in the “engineering” camp have PhDs?

(It’s also possible to label the two groups “experimentalists” vs “theorists”, though for the former I really mean people involved in the construction and day-to-day operations – I’m not interested in semantics here)

While the Higgs was at a sigma of ~4, I heard that postdocs and PhD students at CERN could volunteer for maintenance and similar tasks, and that those who did would have their names on the “Higgs paper” (hence the notoriously large author lists). Was this true and is it still the case?